A classical error channel is built from exact prepared-label counts. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Counts define a classical error channel

Prepared zero gives 18 stays and 2 flips. Prepared one gives 3 flips and 17 stays.

zero row (18,2),one row (3,17)\text{zero row }(18,2),\quad \text{one row }(3,17)
Bit-flip channelCounts are normalized into channel rows.true probabilitieszero 3/4one 1/4assignmentobserved probszero 57/80one 23/80over 80 shots57 zero reads23 one readserror -> read

Prepared-label rows expose both error rates

The channel has a zero-prepared row, a one-prepared row, and a conserved row sum.

preparedpzeroponezero910110one3201720row sum11\begin{array}{c|c|c}\text{prepared}&p_{\text{zero}}&p_{\text{one}}\\\text{zero}&\frac{9}{10}&\frac{1}{10}\\\text{one}&\frac{3}{20}&\frac{17}{20}\\\text{row sum}&1&1\\\end{array}
Bit-flip row scanThe two prepared rows are normalized separately.true probabilitieszero 3/4one 1/4assignmentobserved probszero 57/80one 23/80over 80 shots57 zero reads23 one readserror -> read

The channel changes the count budget

The ideal true budget maps to observed counts 57 and 23 over 80 shots.

Nzero=57,None=23N_{\text{zero}}=57,\quad N_{\text{one}}=23
Bit-flip predictionThe matrix product computes the observed counts.true probabilitieszero 3/4one 1/4assignmentobserved probszero 57/80one 23/80over 80 shots57 zero reads23 one readserror -> read